Why is there a war in Syria?

What began as a peaceful uprising against Syria's President Bashar al-Assad seven years ago became a full-scale civil war that has left more than 340,000 people dead, devastated the country and drawn in global powers.

How did the war begin?

Long before it started, many Syrians complained about high unemployment, widespread corruption, a lack of political freedom and state repression under President Bashar al-Assad, who succeeded his father, Hafez, in 2000.

In March 2011, pro-democracy demonstrations inspired by the Arab Spring erupted in the southern city of Deraa. The government's use of deadly force to crush the dissent soon triggered nationwide protests demanding the president's resignation.

As the unrest spread, the crackdown intensified. Opposition supporters took up arms, first to defend themselves and later to expel security forces from their areas. Mr Assad vowed to crush "foreign-backed terrorism" and restore state control.

The violence rapidly escalated and the country descended into civil war as hundreds of rebel brigades were formed to battle government forces.

Why has the war lasted so long?

In essence, it has become more than just a battle between those for or against Mr Assad.

A key factor has been the intervention of regional and world powers, including Iran, Russia, Saudi Arabia and the United States. Their military, financial and political support for the government and opposition has contributed to the intensification and continuation of the fighting, and turned Syria into a proxy battleground.